I have this nested class
data class UI(
val xPosition: Int,
val yPosition: Int
)
When the Object gets serialized through the #RestController I receive all lowercase on the HTTP endpoint (last line is the interesting one):
{"id":"c8a7b735-b407-4dae-9a41-a470f7596895",
"isActive":false,
"title":"First Sample",
"description":{"shortDescription":"...","longDescription":"...","additionalNotes":"..."},
"endDate":"2021-01-07","priority":0,
"ui":{"xposition":0,"yposition":0}}] <<<<<< see here
I copy the data into a MongoDB document. There it correctly states
ui:
xPosition: 0
yPosition: 0
What is going on here? I cannot get the Spring RestController to return the second letter as uppercase. This destroys the consumption and update of the data in the attached UI :(
Related
I have a class :
class Con {
private List<Ind> inds;
}
I am using Gson in the usual way to convert a JSON string to this class object. so in case, the JSON doesn't have the key inds present this variable inds is assigned a null value. Is there a way to assign inds an empty ArrayList instead?
My Thoughts:
One straightforward way could be once the Gson object is built. Go over all the null objects and assign them to the new ArrayList<>(). Is there a better approach?
public List<Ind> getInds() {
return inds;
}
Currently I am using the above getter in a code like : con.getInds().stream() which is causing NullPointerException.
I am not sure what would be a good way to resolve this. Instead of List Should I return an Optional or Should I modify this getter like
public List<Ind> getInds() {
inds==null?new ArrayList<>():inds;
}
The above will also resolve the NullPointerException. Not sure if there are pros and cons to using this approach. Although now there is no way to identify if the Json has a key with name inds or not. For the current code that I am writing this may not be required. But there is a meaning loss here certainly.
One solution to this would be to assign default values to the fields, for example:
class Con {
private List<Ind> inds = new ArrayList<>();
}
Gson will keep this default value; only if the field is present in the JSON data it will reassign the field value.
There are however a few things to keep in mind:
Your class needs a no-args constructor (implicit or explicit); otherwise Gson might create instances without invoking the initializer blocks of the class, and therefore the field will be null
If the field is present in JSON but has a JSON null value, then Gson will still set that as value
You cannot tell afterwards whether the field was present in JSON but had an empty JSON array as value, or whether it was missing
I'm implementing a policy enforcement point between a client and a server that receives messages from the server, and, if the client doesn't have adequate authorization to see some parts of the message deletes those parts before sending them to the client.
message {
string not_sensitive = 1;
optional string sensitive = 2;
}
pseudo code
from_server >> my_msg;
if (!authorized) {
my_msg.delete("sensitive");
}
to_client << my_msg;
Yes.
As I understand current v3 pb schema language, all fields are optional. But regardless of that, a field marked optional in v2 is something that need not be there. So expanding your pseudo code to, say, C++ (see here), one can see that the generated class would end up with a has_sensitive() method and a clear_sensitive() method. Calling the latter and then serialising the object would result in wire format data that omitted the sensitive field.
Following issue: In a client/server environment with Spring-Boot and Kotlin the client wants to create objects of type A and therefore posts the data through a RESTful endpoint to the server.
Entity A is realized as a data class in Kotlin like this:
data class A(val mandatoryProperty: String)
Business-wise that property (which is a primary key, too) must never be null. However, it is not known by the client, as it gets generated quite expensively by a Spring #Service Bean on the server.
Now, at the endpoint Spring tries to deserialize the client's payload into an object of type A, however, the mandatoryProperty is unknown at that point in time, which would result in a mapping exception.
Several ways to circumvent that problem, none of which really amazes me.
Don't expect an object of type A at the endpoint, but get a bunch of parameters describing A that are passed on until the entity has actually been created and mandatoryProperty is present . Quite cumbersome actually, since there are a lot more properties than just that single one.
Quite similar to 1, but create a DTO. One of my favorites, however, since data classes can't be extended it would mean to duplicate the properties of type A into the DTO (except for the mandatory property) and copy them over. Furthemore, when A grows, the DTO has to grow, too.
Make mandatoryProperty nullable and work with !! operator throughout the code. Probably the worst solution as it foils the sense of nullable and non-nullable variables.
The client would set a dummy value for the mandatoryProperty which is replaced as soon as the property has been generated. However, A is validated by the endpoint and therefore the dummy value must obey its #Pattern constraint. So each dummy value would be a valid primary key, which gives me a bad feeling.
Any other ways I might have overseen that are more feasible?
I don't think there is a general-purpose answer to this... So I will just give you my 2 cents regarding your variants...
Your first variant has a benefit which no other really has, i.e. that you will not use the given objects for anything else then they were designed to be (i.e. endpoint or backend purposes only), which however probably will lead to cumbersome development.
The second variant is nice, but could lead to some other development errors, e.g. when you thought you used the actual A but you were rather operating on the DTO instead.
Variant 3 and 4 are in that regard similar to 2... You may use it as A even though it has all the properties of a DTO only.
So... if you want to go the safe route, i.e. no one should ever use this object for anything else then its specific purpose you should probably use the first variant. 4 sounds rather like a hack. 2 & 3 are probably ok. 3 because you actually have no mandatoryProperty when you use it as DTO...
Still, as you have your favorite (2) and I have one too, I will concentrate on 2 & 3, starting with 2 using a subclass approach with a sealed class as supertype:
sealed class AbstractA {
// just some properties for demo purposes
lateinit var sharedResettable: String
abstract val sharedReadonly: String
}
data class A(
val mandatoryProperty: Long = 0,
override val sharedReadonly: String
// we deliberately do not override the sharedResettable here... also for demo purposes only
) : AbstractA()
data class ADTO(
// this has no mandatoryProperty
override val sharedReadonly: String
) : AbstractA()
Some demo code, demonstrating the usage:
// just some random setup:
val a = A(123, "from backend").apply { sharedResettable = "i am from backend" }
val dto = ADTO("from dto").apply { sharedResettable = "i am dto" }
listOf(a, dto).forEach { anA ->
// somewhere receiving an A... we do not know what it is exactly... it's just an AbstractA
val param: AbstractA = anA
println("Starting with: $param sharedResettable=${param.sharedResettable}")
// set something on it... we do not mind yet, what it is exactly...
param.sharedResettable = UUID.randomUUID().toString()
// now we want to store it... but wait... did we have an A here? or a newly created DTO?
// lets check: (demo purpose again)
when (param) {
is ADTO -> store(param) // which now returns an A
is A -> update(param) // maybe updated also our A so a current A is returned
}.also { certainlyA ->
println("After saving/updating: $certainlyA sharedResettable=${certainlyA.sharedResettable /* this was deliberately not part of the data class toString() */}")
}
}
// assume the following signature for store & update:
fun <T> update(param : T) : T
fun store(a : AbstractA) : A
Sample output:
Starting with: A(mandatoryProperty=123, sharedReadonly=from backend) sharedResettable=i am from backend
After saving/updating: A(mandatoryProperty=123, sharedReadonly=from backend) sharedResettable=ef7a3dc0-a4ac-47f0-8a73-0ca0ef5069fa
Starting with: ADTO(sharedReadonly=from dto) sharedResettable=i am dto
After saving/updating: A(mandatoryProperty=127, sharedReadonly=from dto) sharedResettable=57b8b3a7-fe03-4b16-9ec7-742f292b5786
I did not yet show you the ugly part, but you already mentioned it yourself... How do you transform your ADTO to A and viceversa? I will leave that up to you. There are several approaches here (manually, using reflection or mapping utilities, etc.).
This variant cleanly seperates all the DTO specific from the non-DTO-specific properties. However it will also lead to redundant code (all the override, etc.). But at least you know on which object type you operate and can setup signatures accordingly.
Something like 3 is probably easier to setup and to maintain (regarding the data class itself ;-)) and if you set the boundaries correctly it may even be clear, when there is a null in there and when not... So showing that example too. Starting with a rather annoying variant first (annoying in the sense that it throws an exception when you try accessing the variable if it wasn't set yet), but at least you spare the !! or null-checks here:
data class B(
val sharedOnly : String,
var sharedResettable : String
) {
// why nullable? Let it hurt ;-)
lateinit var mandatoryProperty: ID // ok... Long is not usable with lateinit... that's why there is this ID instead
}
data class ID(val id : Long)
Demo:
val b = B("backend", "resettable")
// println(newB.mandatoryProperty) // uh oh... this hurts now... UninitializedPropertyAccessException on the way
val newB = store(b)
println(newB.mandatoryProperty) // that's now fine...
But: even though accessing mandatoryProperty will throw an Exception it is not visible in the toString nor does it look nice if you need to check whether it already has been initialized (i.e. by using ::mandatoryProperty::isInitialized).
So I show you another variant (meanwhile my favorite, but... uses null):
data class C(val mandatoryProperty: Long?,
val sharedOnly : String,
var sharedResettable : String) {
// this is our DTO constructor:
constructor(sharedOnly: String, sharedResettable: String) : this(null, sharedOnly, sharedResettable)
fun hasID() = mandatoryProperty != null // or isDTO, etc. what you like/need
}
// note: you could extract the val and the method also in its own interface... then you would use an override on the mandatoryProperty above instead
// here is what such an interface may look like:
interface HasID {
val mandatoryProperty: Long?
fun hasID() = mandatoryProperty != null // or isDTO, etc. what you like/need
}
Usage:
val c = C("dto", "resettable") // C(mandatoryProperty=null, sharedOnly=dto, sharedResettable=resettable)
when {
c.hasID() -> update(c)
else -> store(c)
}.also {newC ->
// from now on you should know that you are actually dealing with an object that has everything in place...
println("$newC") // prints: C(mandatoryProperty=123, sharedOnly=dto, sharedResettable=resettable)
}
The last one has the benefit, that you can use the copy-method again, e.g.:
val myNewObj = c.copy(mandatoryProperty = 123) // well, you probably don't do that yourself...
// but the following might rather be a valid case:
val myNewDTO = c.copy(mandatoryProperty = null)
The last one is my favorite as it needs the fewest code and uses a val instead (so also no accidental override is possible or you operate on a copy instead). You could also just add an accessor for the mandatoryProperty if you do not like using ? or !!, e.g.
fun getMandatoryProperty() = mandatoryProperty ?: throw Exception("You didn't set it!")
Finally if you have some helper methods like hasID(isDTO or whatever) in place it might also be clear from the context what you are exactly doing. The most important is probably to setup a convention that everyone understands, so they know when to apply what or when to expect something specific.
I am working on a package that uses RJava for identifier mapping (in biology): BridgeDbR. One of the methods calls a Java method which has vargs, mapID():
xref <- .jnew("org/bridgedb/Xref", identifier, datasource)
datatarget <- getDataSource(code=target)
targets = .jarray(c(datatarget), contents.class="org/bridgedb/DataSource")
Here the getDataSource() method returns a Java object of type org.bridgedb.DataSource.
The actual call of interest is then made like, where (as shown above) xref and targets are Java object, and where mapper is also Java object, see below:
mappings = mapper$mapID(xref, targets)
This mapper object is an instance of the IDMapper interface and defines the mapID() method using vargs:
public Set<Xref> mapID (Xref ref, DataSource... tgtDataSources)
throws IDMapperException;
Now, I want to call this method without data sources. In Java I would just do:
someMapper.mapID(someXref)
... and Java find this method.
However, I cannot figure out how to do this in RJava. The following variants all do not work (e.g. .jarray(c(), contents.class="org/bridgedb/DataSource") return NULL):
mappings = mapper$mapID(xref, c())
mappings = mapper$mapID(xref)
mappings = mapper$mapID(xref, NULL)
mappings = mapper$mapID(xref, .jarray(c(), contents.class="org/bridgedb/DataSource"))
The output of .jmethods(mapper, name="mapID") is:
[1] "public java.util.Set org.bridgedb.rdb.SimpleGdbImplCommon.mapID(org.bridgedb.Xref,org.bridgedb.DataSource[]) throws org.bridgedb.IDMapperException"
[2] "public java.util.Map org.bridgedb.rdb.IDMapperRdb.mapID(java.util.Collection,org.bridgedb.DataSource[]) throws org.bridgedb.IDMapperException"
How can I call this Java method (mapper$mapID) with RJava with just the xref?
As pointed out in https://www.rforge.net/doc/packages/rJava/jarray.html, you should supply a list in the call to .jarray, possibly with a single NULL element
I'm building an web application using Spring 3.0 MVC.
I have a method which has prototype below.
#RequestMapping(value = "/blahblah/blah.do", method=RequestMethod.GET)
public void searchData(#RequestParam(value="uniqOid", required=false) String uniqOid, #ModelAttribute("MasterVo") MasterVo searchVo,
ModelMap model, HttpServletResponse response, HttpServletRequest request)
The problem is that, the view (jsp) contains inputs that matches to searchVo(ModelAttribute).
When the int or long value of searchVo didn't come from the jsp, the server throws 404 page not found exception.
If the type of value is "String", it has no problem.
In my opinion, it is the problem of type casting.
How could I solve this problem, and which part of the server code that I have to check?
Thanks in advance.
I will go ahead and assume a few things about your problem.
It is not a type-cast problem. Spring has default converters that can easily convert from a String to some primitive type.
Now what you are facing is I think a null assigment to primitive type problem. Suppose the name of the property that's causing the problem is named primitiveProperty. Now, the request-paramters could include a parameter named primitiveProperty with an empty-String value, or some value that cannot be converted to a number. If the type of the primitiveProperty is String, it can assign the value of that parameter to it without any problem.
If the type of the primitiveProperty is int, long or some other primitive type that cannot have a null value, a problem occurs. When Spring converts the empty-string or a non-numeric string valued request-param named primitiveProperty, it cannot do so since that string can't be converted to a valid int or long value. So it is converted to null. Now, when Spring tries to assign that null value to a property that cannot have a null value (any primitve type), you get an Exception. If you are getting an empty-string as your request-param, you can replace the troublesome property in your domain object with its equivalent wrapper class (int with Integer, long with Long and so on). If you are getting a non-numeric value from your view, well, make sure that you don't get a non-numeric value.
You need to check the setter of the fields that are giving the typecast problem, in your case MasterVo .
The Spring will call the setter of the property to bind the value, where i presume you will see the error coming.
Just add a debug point to this setter and you will see the problem.